Re: [PATCH 3/3] drm/gem-shmem: Track folio accessed/dirty status in vmap

[Boris Brezillon <boris.brezillon@collabora.com>]

On Tue, 27 Jan 2026 14:16:38 +0100
Thomas Zimmermann <tzimmermann@suse.de> wrote:

> On successful vmap, set the page_mark_accessed_on_put and _dirty_on_put
> flags in the gem-shmem object. Signals that the contained pages require
> LRU and dirty tracking when they are being released back to SHMEM. Clear
> these flags on put, so that buffer remains quiet until the next call to
> vmap. There's no means of handling dirty status in vmap as there's no
> write-only mapping available.
> 
> Both flags, _accessed_on_put and _dirty_on_put, have always been part of
> the gem-shmem object, but never used much. So most drivers did not track
> the page status correctly.
> 
> Only the v3d and imagination drivers make limited use of _dirty_on_put. In
> the case of imagination, move the flag setting from init to cleanup. This
> ensures writeback of modified pages but does not interfere with the
> internal vmap/vunmap calls. V3d already implements this behaviour.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>

The gem-shmem changes are

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c | 4 ++++
>  drivers/gpu/drm/imagination/pvr_gem.c  | 6 ++++--
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 30cd34d3a111..8c07a8f81322 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -265,6 +265,8 @@ void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
>  				  shmem->pages_mark_dirty_on_put,
>  				  shmem->pages_mark_accessed_on_put);
>  		shmem->pages = NULL;
> +		shmem->pages_mark_accessed_on_put = false;
> +		shmem->pages_mark_dirty_on_put = false;
>  	}
>  }
>  EXPORT_SYMBOL_GPL(drm_gem_shmem_put_pages_locked);
> @@ -397,6 +399,8 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
>  		} else {
>  			iosys_map_set_vaddr(map, shmem->vaddr);
>  			refcount_set(&shmem->vmap_use_count, 1);
> +			shmem->pages_mark_accessed_on_put = true;
> +			shmem->pages_mark_dirty_on_put = true;
>  		}
>  	}
>  
> diff --git a/drivers/gpu/drm/imagination/pvr_gem.c b/drivers/gpu/drm/imagination/pvr_gem.c
> index c07c9a915190..307b02c916d4 100644
> --- a/drivers/gpu/drm/imagination/pvr_gem.c
> +++ b/drivers/gpu/drm/imagination/pvr_gem.c
> @@ -25,7 +25,10 @@
>  
>  static void pvr_gem_object_free(struct drm_gem_object *obj)
>  {
> -	drm_gem_shmem_object_free(obj);
> +	struct drm_gem_shmem_object *shmem_obj = to_drm_gem_shmem_obj(obj);
> +
> +	shmem_obj->pages_mark_dirty_on_put = true;
> +	drm_gem_shmem_free(shmem_obj);
>  }
>  
>  static struct dma_buf *pvr_gem_export(struct drm_gem_object *obj, int flags)
> @@ -363,7 +366,6 @@ pvr_gem_object_create(struct pvr_device *pvr_dev, size_t size, u64 flags)
>  	if (IS_ERR(shmem_obj))
>  		return ERR_CAST(shmem_obj);
>  
> -	shmem_obj->pages_mark_dirty_on_put = true;
>  	shmem_obj->map_wc = !(flags & PVR_BO_CPU_CACHED);
>  	pvr_obj = shmem_gem_to_pvr_gem(shmem_obj);
>  	pvr_obj->flags = flags;